Processes for the production of p-vinyl phenol which comprise (1) dehydrating p-acetoxyphenyl-methyl carbinol; (2) decomposing p-hydroxycinnamic acid by decarbonation; (3) decomposing bisphenol ethane; and (4) dehydrogenating p-ethyl phenol, etc., are well known.
However, the crude p-vinyl phenol obtained from the above-described processes contains a large amount of impurities such as phenols that do not have any unsaturated side chains, e.g., phenol, cresol or ethyl phenol, etc. Further, it is very difficult to obtain p-vinyl phenol having high purity by purification of the resulting crude p-vinyl phenols.
It has been known that p-vinyl phenol will polymerize even in the presence of phenols that do not have any unsaturated side chains such as phenol, cresol or ethyl phenol, etc. A process for the production of a p-vinyl phenol polymer which comprises polymerizing crude p-vinyl phenol containing such phenols as impurities without carrying out purification of the crude p-vinyl phenol is disclosed in Japanese Patent Publication (unexamined) No. 13694/78.
It has also been known that both phenols that do not have any unsaturated side chains and water serve as molecular weight regulators for the desired polymer when carrying out polymerization of p-vinyl phenol. A process which comprises polymerizing p-vinyl phenol using such phenols or water as a molecular weight regulator to obtain a p-vinyl phenol polymer having a desired molecular weight is disclosed in Japanese Patent Publication (unexamined) No. 44609/82.
The above-described processes for the production of a p-vinyl phenol polymer which comprise polymerizing p-vinyl phenol in the presence of phenols that do not have any unsaturated side chains are not satisfactory for the following reasons. If phenols that do not have any unsaturated side chains, such as phenol, cresol or ethyl phenol, etc., are present in the polymerization reaction system when carrying out polymerization of p-vinyl phenol, low molecular weight by-products, e.g., dimers or trimers, having the form that the benzene nucleus of the phenols that do not have any unsaturated side chains are substituted by p-vinyl phenol, are formed in addition to the polymer of p-vinyl phenol. Thus, these low molecular weight by-products are contained in the desired p-vinyl phenol polymer.
The p-vinyl phenol polymer has been viewed as a functional high polymer material since its reactivity, due to its phenolic hydroxyl groups, is different from that of polystyrene. Further, its properties are different from those of phenol resin due to the vinyl bonds. However, if the low molecular weight by-products, as described above, are present in the p-vinyl phenol polymer, they have a bad influence upon the properties of the p-vinyl phenol polymer, for example, they cause deterioration of heat resistance. Accordingly, it is necessary to minimize the content of the low molecular weight by-products in the p-vinyl phenol polymer.
In order to reduce the content of the low molecular weight by-products in the resulting p-vinyl phenol polymer, it is necessary, when carrying out the polymerization reaction, to prevent side reactions that form the low molecular weight by-products or to remove the low molecular weight by-products from the polymer after conclusion of the polymerization reaction.
One process for removing the low molecular weight by-products after conclusion of the polymerization reaction comprises carrying out reprecipitation or washing with a solvent which does not dissolve the polymer but dissolves the low molecular weight by-products. Another process comprises removing the low molecular weight by-products by reduced pressure distillation.
However, the above-described processes are complicated and expensive because the physical properties of the low molecular weight by-products are similar to those of low molecular weight fractions of the desired polymers. Further, formation of the low molecular weight by-products causes a loss of p-vinyl phenol.
Accordingly, it is desired to control the side-reactions that form the low molecular weight by-products when carrying out the polymerization reaction to such an extent so that these by-products do not interfere with the practical use of the resulting polymer.